@tomic601 I also have an ARC Ref 5SE and love it. But if you haven't replaced the tubes for 6000 hours you should really do that. The 6H30 and 6550 tubes are cheap and the manual recommends replacing them every 4000 hours. It is likely that there has been a slight degradation in the sound quality and you just haven't noticed it.
Audio Research Pre-Amp advice
Hi, what would be a good used Audio Research pre-amp that has a remote, that is overall very musical. My budget is under 6K? I really don't want any Ref. pre's because too many tubes. Also something not too old, I do not want to have to bring in for service. I welcome and appreciate any advice. Thank you!